Neurons in very few CNS populations continue to be produced during adulthood. The goal of our research is to understand the function of this adult neurogenesis by studying the regulation of neuronal precursor proliferation and survival. This year we published an investigation of the synaptic maturation of newborn granule neurons in the adult dentate gyrus, a part of the hippocampal region in which large numbers of new neurons are born throughout adulthood. We examined GABAergic synaptic responses in immature granule cells, determining that they were less frequent and had slower kinetics than GABAergic responses in mature granule cells. Using pharmacology, we found evidence for a developmental switch in the subtype of GABAA receptors expressed by granule cells born in adulthood. In addition, we found that GABA depolarizes young granule cells ? the opposite of the response to GABA in mature granule cells ? suggesting that firing of inhibitory interneurons has very different effects on immature granule cells than it has on neighboring mature granule cells. We also began a study aimed at understanding the effects of spatial learning on activation and survival of young granule cells.